Field of the Invention
This invention relates to electrostatic discharge (ESD) and ESD protection associated with baluns.
Description of the Related Art
FIG. 1 illustrates a portion of a radio frequency (RF) system that includes an integrated circuit 101 with an output stage 103 and a balun 105. Baluns may be used to convert single-ended signals into differential signals or differential signals into single ended signals. Baluns may also be used to reject even harmonics and as band-select filters. Bond wires 107 couple the balun to an antenna 109 through package output terminals (pins) 108 and 110. In the example of FIG. 1, the balun comprises a transformer that includes an input coil 115 and an output coil 117. The number of turns in the illustrated RF system is the same in each coil although the ratio of turns in each coil can be different according to system requirements.
The signals on terminals 108 and 110 are supplied to front-end module (FEM) 112, which in turn drives antenna 109. Typically, an FEM includes an input matching network to match the impedance to the driver power amplifier (PA), and/or includes another PA to get more power gain, and/or another low noise amplifier (LNA) to improve the noise figure of the received signal, and/or a matching network to match to the antenna 109.
The bond wires 107 include an inductance that provides impedance at high frequencies. Thus, significant voltage swings occur on terminals outp and outn as part of normal RF operation, e.g., a voltage swing of between −4 and +4 volts. Conventional ESD protection circuits operate at frequencies comparable with normal balun operation and can interfere with balun operation. Thus, a conventional ESD protection circuit could respond to balun voltage/current swings as an ESD event and clamp to ground. That is undesirable since it will result in excessive leakage to ground during normal operation and possibly power loss.
Since ESD events can impact package terminals 108 and 110, avoiding ESD damage due to ESD events for the package terminals associated with the balun is needed, while still ensuring the ESD protection avoids interference with normal operation.